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In a Falcon 9 launch, the second stage looks like it achieves orbit along with the payload. But is that impression accurate? Does SpaceX need to do anything to deorbit the stage?
I can see a few possibilities, but haven't been able to find which one's correct:
There's actually a few outcomes of the second stage that can occur (and some interesting tales to go along with them), but as geoffc has mentioned, second stage reuse is no longer planned for Falcon as Musk thinks the resources to develop it are better spent elsewhere. It's not an insurmountable technical challenge.
This is done for missions where the upper stage has enough remaining fuel reserves to ensure an intentional decay can occur safely. This has been done on every LEO mission since CRS-3 (including Orbcomm OG2), and usually results in the stage being deorbited Southsouthwest of Australia in the Indian Ocean (close to the area where MH370 was lost). We know this because occasionally SpaceX will post a NOTAM declaring the zone unsafe for a certain time. Here's the CRS-3 NOTAM, for example:
So far, this has been standard operating procedure for all 4 Falcon 9 upper stages that have delivered communications satellites to GTO. At this time, none remain in orbit, as the periapsis of each is so low (~200-300km) that they decay within 2-6 months. No deorbit profile has been attempted as it presents SpaceX with a liability if the stage decides to explode, scattering debris in GTO (additionally, if not enough fuel remains, they cannot safely deorbit either).
The standard apoapsis for GTO is about 35,000km, but for the first two GTO missions (SES-8 & Thaicom 6), they were injected into what is known as a "Supersynchronous Orbit" with an apoapsis beyond 35,000km. In the latter, it was in excess of 90,000km. It was launched on January 6 and decayed May 28.
You'd also expect the stage to disintegrate upon reentry, wouldn't you. Not always! The upper stage of AsiaSat 6 reentered over Brazil and parts of it were found scattered in an open field. It made quite the fireworks on reentry though:
Some of the largest items found intact were the Composite Overwrapped Pressure Vessels (COPV's), which stored helium.
This has been the case for Falcon 1 Flights 4 & 5 which remain in a nearly equatorial LEO to this day, as well as the first 5 Falcon 9 flights - of which COTS1 performed an unannounced upper stage restart boosting it into a 290x10,700km orbit & CASSIOPE, which attempted a "sideways" upperstage restart which failed, stranding it in a 900km polar orbit.
This hasn't happened yet, but the next mission, launching DSCOVR (currently scheduled for January 29, likely to be delayed), will see the upperstage place the 570kg payload in Earth-Sun L1, before entering a solar orbit, becoming the first piece of SpaceX hardware to leave Earth's orbit.
<crackpot>SW of Australia? Clearly MH-370 intercepted a deorbiting second stage and used it to refuel (RP-1 and Jet-A basically same thing, look it up) and get to superseekret Antarctic base to communicate with the Roswell Greys.</crackpot>
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It depends on trajectory.
A mission to LEO obviously leaves the second stage in a very different orbit than a GEO mission, where perhaps they boosted to some odd 80,000M X 250M orbit, where the satellite bus will correct the orbit after it is done with the second stage.
SpaceX would love to recover the second stage, which they had planned. But it sounds like they have given up on that.
Transcript - Elon Musk at MIT's Aero/Astro Centennial (part 1 of 6)
[What about the second stage?] The next generation vehicles after the Falcon architecture will be designed for full reusability. I don't expect the Falcon 9 to have a reusable upper stage, just because the - with a kerosene-based system, the specific impulse isn't really high enough to do that, and a lot of the missions we do for commercial satellite deployment are geostationary missions. So, we're really going very far out. These are high delta-velocity missions, so to try to get something back from that is really difficult.
Reality bit them harder than expected, and they are focused on the next booster (BFR - Big F-ing Rocket, using Raptor engines) and its second stage for reuse.
A second stage left in LEO orbit is very easy to deorbit and most likely would on its own fairly quickly.
A second stage left in GTO (GEO Transfer Orbit) is a different kettle of fish. If it is left in a highly elliptical transfer orbit, it usually has a fairly low perigee, which means minor alterations at the low point can force a reentry.
There is a Reddit page that tracks the current location of the various second stages left in orbit from GTO launches. Table of Second stages
SpaceX's second stages probably always achieve orbit. Typically they do a post-deployment burn to deorbit the stage, although they don't always do that. I know most/all LEO missions are done that way, I'm not sure about GEO missions. Basically, if they can deorbit it deliberately, they will.
